Refrigeration system with oil return means



April 15, 1969 E. E. ONEIL 3,438,218

REFRIGERATION SYSTEM WITH OIL RETURN MEANS Filed Sept. 13. 1967 v INVENTOR. Eugene E. O'Neil BY amaz mmm gw ATTORNEYS United States Patent 3,438,218 REFRIGERATION SYSTEM WITH OIL RETURN MEANS Eugene E. ONeil, Marshalltown, Iowa, assignor to Duuham-Bush, Inc., West Hartford, Coma, a corporation of Delaware Filed Sept. 13, 1967, Ser. No. 667,399 Int. Cl. F25!) 41/04, 43/02 US. Cl. 62-218 9 Claims ABSTRACT OF THE DISCLOSURE This invention relates to refrigeration systems, and more in particular to returning the oil with the suction gas from the evaporator to the compressor, and to such systems having evaporators with vertical refrigerant tubes.

An object of this invention is to provide an improved arrangement for returning the oil to the compressor from the evaporator of a refrigeration system utilizing heavier than oil refrigerants. Another object is to provide an improved vertical tube evaporator for refrigeration systems. A further object is to provide improved operation of refrigeration systems having vertical, fluid-cooling evaporators. Another object is to provide for the above with a system which is operated with wide variations in load. A further object is to provide for the above in a manner which is efficient and dependable, and wherein the structure is simple, compact, inexpensive to manufacture, and adaptable to various conditions of operation and use. These and other objects will be in part obvious and in part pointed out below.

In the drawings:

FIGURE 1 is a somewhat schematic view of one embodiment of the invention; and

FIGURE 2 is a greatly enlarged showing of the central portion of FIGURE 1, with the dimensions of the parts being represented in relative proportions.

Referring to FIGURE 1 of the drawings, a refrigeration system has a compressor 2, a compressed gas line 3, a condenser '4, a receiver 6, a liquid line 7, an automatic metering valve 8 which acts as a restrictor to reduce the pressure, an evaporator 10, a suction tube assembly 11 extending from the top of the evaporator, and a suction line 12. Evaporator 10 is of the vertical tube and shell type, with a vertical shell :13 formed by a cylinder and end bells. Within shell :13 there is a bottom header 14 between a bottom tube sheet 15 and the bottom end bell, and a top dome chamber 16 above a top tube sheet 18.

Dome chamber 16 acts as a top header and provides a zone within which the refrigerant gas separates from the liquid refrigreant and the oil. The oil is lighter than the liquid refrigerant and tends to produce foam above tubes 20. The refrigerant tubes 20 are mounted between the tube sheets and are flooded so that the liquid level is substantially above the top of tube sheet 18 in the bottom of dome chamber .16. The fluid to be cooled is delivered to shell 13 through a line 22 directly below tube sheet 18, and the cooled fluid is withdrawn through a line 24 directly above tube sheet 15. Hence, the fluid to be cooled flows downwardly, although for some conditions of op- "ice eration the flow may be upwardly, i.e., it may enter at line 24 and leave at line 22. With either direction of flow, the entire space within the cylindrical shell between the tube sheets and around the tubes acts as the fluid-cooling chamber.

Projecting downwardly into dome chamber 16 from the top end bell of shell 13, and concentric with the shell, is the suction tube assembly 11 which is formed by a metal tube 32 and a pair of sheet metal baffles 36 and 38 rigidly welded thereon. At its upper end, tube 32 has an extension 30 which extends horizontally and thence downwardly, where it is connected to the suction line 112 extending to the compressor. The bottom end of tube 32 (see also FIGURE 2) has a pair of inverted V-notches 42 which are diametrically spaced (at the right and left in FIGURE 2) so that the tube has two diametrically spaced end portions 47 (FIGURE 1) terminating at edges 48. Each of the bafiies is an inverted frustrum of a cone, with its lower extremity snugly hugging the tube, except where baffle 38 extends across the V-notches 42, and directly above each of the V-notches where there is a slot 39 in the upper bafile 36. Battle 36 collects oil upon its surfaces, and the oil flows downwardly along the outer surface of tube 32. The oil collected above the baffle flows through slots 39 downwardly in flat streams directly toward V-notches 42. The oil collected by the upper surfaces of baffle 38 is also directed toward the edges of.

the V-notches.

Mounted upon the top tube sheet 18 and concentric with shell 13 and tube assembly 11 is a skimmer cup 44, the top of which surrounds the extreme lower end portions 47 of tube 32. Extending downwardly from the top edge of the skimmer cup are two diametrically spaced V-notches 54 (at the right and left in FIGURE 1), the apexes of which extend below the lower edges 48- of tube 32. Hence, the skimmer cup provides a central chamber at the bottom end of tube 32 which is open only at the top around the tube and at the V-notches 54 upon opposite sides and adjacent the respective end portions 47 of tube 32.

Mounted in the side wall of shell 13 and opening into dome .16 is a well 64 in which is positioned the bulb 66 of a control unit for valve 8. The outwardly projecting end of well 64 is vented to dome 16 by a vent-tube 72. As will be explained more fully below, control unit 60 contains an electrical heating element and receives electric current through a line 70. Referring to FIGURE 2, the bottom edge '65 of bulb 66 is in horizontal alignment with the apexes 56 of V-notches 54. The control point of bulb 66 is on a line 67 which is spaced upwardly from edge one-quarter of the distance to the top of the bulb. The temptrature at the control point is the temperature to which the control assembly 60 is responsive, and the control point is at a level slightly below the top edge 45 of the skimmer cup. During normal operation, the general liquid level of refrigerant is at line 67, and the range in the level may be between line 67 and the bottom edge 54 of baffle 38.

During the upward flow of refrigerant through evaporator tubes 20, the refrigerant evaporates and causes foaming of the oil which tends to accumulate above the tube sheet 18. However, the evaporator tubes are in an annular Zone, as there are no tubes beneath the skimmer cup. The foam tends to form and rise in the area around the skimmer cup, with the refrigerant gas being freed and passing upwardly into the dome. The refrigerant gas then passes downwardly above baffle 38 and into tube 32 through the V-notches 42. Battle 38 deflects the rising foam and refrigerant outwardly, so that liquid refrigerant is not thrown into the zone above baflie 38. Hence, slugging is prevented. As will be explained more fully below,

the refrigerant gas entering tube 32 picks up the oil and carries it back to the compressor.

Simultaneously with the movement of the refrigerant gas and foam upwardly around the skimmer cup and baffle 38, there is a general flow radially inwardly toward the top of the skimmer cup, with the result that the separated oil tends to accumulate in the skimmer cup and beneath baflie 38. Also, action of baffle 38 in deflecting the foam aids oil in separating out, and it flows downwardly toward the skimmer cup. The skimmer cup acts as a submerged annular baffle and produces a central zone above the tube sheet and beneath the tube assembly. Within that zone there is less turbulence than in the surrounding zone, and at light loads the liquid may be relatively quiescent. Due to the fact that the oil is lighter than the liquid refrigerant, the liquid refrigerant tends to form a layer along the tube plate 18, and the oil collects in the vicinity of the top of the skimmer cup and around the bottom of baffle 38.

The fluid being cooled flows directly beneath the tube sheet 18 which forms the bottom of the skimmer cup, and heat is transferred upwardly through the tube sheet. The heat produces evaporation of liquid refrigerant in the skimmer cup, thus increasing the concentration of oil and causing turbulence tending to throw the oil upwardly into the bottom of tube 32. Such turbulence is not sufficient to cause drops of liquid refrigerant to enter the tube, but it can aid the entrainment of the oil in the stream of refrigerant gas.

It has been pointed out above, that control unit 60 controls the operation of valve 8, and for that purpose bulb 66 is connected to the valve by a capillary tube 68. Control unit 60 includes a heater element (not shown) which receives electric current through supply cord or line 70, and which constantly adds a predetermined amount of heat to bulb 66, and refrigerant gas which is formed in well 64 is vented to dome 16. Hence, liquid refrigerant flows radially inwardly along chamber 64 around bulb 66, and simultaneously the bulb is heated at a constant rate. If the liquid refrigerant is at the desired level, the bulb is cooled at the proper rate to maintain a heat balance, and there is no change in rate at which liquid re frigerant flows through valve 8. However, if the liquid level is lower than desired, the bulb temperature rises and valve 8 is opened to increase the rate of supply of refrigerant to the evaporator. If the liquid level is higher than desired, the bulb tem erature is reduced below that desired so that valve 8 reduces the rate of refrigerant flow to the evaporator. The liquid level in the bottom of dome chamber 16 is therefore maintained within acceptable limits, and the level is changed by regulating control unit 60. 1

It has been explained above that oil is drawn upwardly through the suction tube assembly 11, and it then flows horizontally through extension 30 and thence downwardly to the suction line 12. The upper portions of V-notches 42 are maintained free of liquid refrigerant, so that there is 'a free passageway for the refrigerant gas flowing downwardly above baffle 38 and into tube 32. When the liquid level is below the bottom of baflie 38, refrigerant gas also enters tube 32 through the lower portions of V-notches 42 between the end portions 47 of the tube. With all conditions of operation, the rapidly-moving streams of gas pick up the oil from the bafile and tube surfaces and from the top surface of the layer of oil in the vicinity of the notches. However, no unevaporated refrigerant is returned to the compressor.

Directly below the top wall of shell 13, tube 32 has two small openings 72 through which refrigerant gas is withdrawn constantly. Openings 72 act to constantly purge the dome chamber of non-condensable gases which might otherwise accumulate and interfere with the operation. Such non-condensable gases are accumulated elsewhere in the system and are purged in the normal manner.

In the system of the illustrative embodiment, an arrangement is provided for maintaining proper operating conditions even at very light loads. By this arrangement a stream of hot gas is supplied to the top of dome 16 when the suction pressure drops below a predetermined value, in accordance with the system of US. Patent No. 2,945,355 of Cecil Boling, so as to maintain a somewhat constant volume of gas pumped. For that purpose there is a hot refrigerant gas line 92 extending from compressed gas line 3 to a normally-closed automatic control valve 94, and the valve 94 is connected through a line 96 to the top of dome 16. Valve 94 opens in response to a drop in the refrigerant pressure on its downstream side, thus to permit hot refrigerant gas to flow into the top of the dome. Hence, when there is a drop in the loadon the refrigeration system of a magnitude suflicient to cause the suction pressure to drop below a predetermined value, valve 94 starts to open, and it delivers a stream of hot compressed gas directly into the dome. Line 96 directs the stream of hot gas toward the top of baflie 36 so as to cause turbulence of the gas and to thoroughly mix the hot gas with the cold refrigerant gas in the dome. The turbulence also has the effect of reducing the foaming within the dome, and it also aids in separating the oil within the vicinity of bafiie 38. The hot gas also aids in evaporating any droplets of liquid refrigerant which are thrown upwardly above the general level of the liquid in the bottom of the dome. With this arrangement, the compressed gas increases the pressure and temperature within the dome chamber to produce an equilibrium condition, and the volume of gas pumped is always sufiicient to return the oil from the skimmer cup.

In the illustrative embodiment of the present invention, the refrigeration system is used to condense refrigerant so that a substantial volume of gas passes into the fluidcooling chamber through line 22, and liquid refrigerant is withdrawn through line 24. The space surrounding the tubes is provided with horizontal bafiies which increase the flow path of the fluid being cooled. When liquid is cooled, the flow may be from the top of the evaporator to the bottom, or in the reverse. It is significant, however, that the vertical evaporator tubes are maintained at substantially the same temperature throughout. Certain specific dimensions and operating conditions are disclosed above and in the attached drawings. For example, the V-notches in tube 32 and in the skimmer cup 44 are 60 notches. Also, the refrigeration system includes the standard control components and auxiliaries. However, it is understood that variations may be made without departing from the scope of the invention as defined in the claims.

What is claimed is:

1. In a refrigeration system which includes a compressor and an evaporated and wherein oil accompanies the refrigerant to the evaporator and must be returned to the suction line of the compressor, the combination of, an evaporator of the type which is flooded with liquid refrigerant throughout the evaporator space which constitutes the cooling zone, means forming a gas and liquid separation chamber at a level above said evaporator space within which a body of liquid may be maintained which is in direct liquid flow relationship with the refrigerant in said evaporator zone, said chamber also having a gas space to which the refrigerant passes from said evaporator zone, control means to maintain a desired level of liquid in said liquid collecting space, oil separating means including means forming an oil-collection Zone and baffle means at an angle to the horizontal having an upwardly exposed surface which directs oil moving downwardly into said oil-collection zone said baflie means having a downwardly exposed surface which directs refrigerant and foam which passes upwardly from the level of said liquid-collecting space away from said oil-collection zone, and suction tube means having a suction gas inlet opening above the bottom of said upwardly exposed surface and open above said bafiie means to withdraw refrigerant gas from said chamber with the gas flow being in fluid-moving relationship to the oil in said oil-collection Zone to entrain the oil and to direct it along a flow path toward the compressor.

2. Apparatus as described in claim 1 wherein said evaporator is of the shell and tube type having vertically extending refrigerant tubes and having a tube sheet in which the refrigerant tubes are mounted and which forms the bottom wall of said chamber whereby there is a body of liquid refrigerant and oil above said tube sheet and within said chamber.

3. Apparatus as described in claim 2 wherein said suction tube means includes a vertical tube extending downwardly with its lower end in said oil-collection zone and wherein said gas inlet opening includes a vertically extending notch having its upper portion above said desired level and the lower edge of said baffle means and with its lower portion below the lower edge of said baflie means.

4. Apparatus as described in claim 3 wherein said vertical tube projects from said chamber substantially in vertical alignment with said oil-collection space, and which includes two invested frusto-conical oil-collecting baffles mounted upon said vertical tube.

5. Apparatus as described in claim 4 wherein said oil separating means includes a skimmer cup concentrically positioned at the lower portion of said vertical tube and having V-slots substantially at said desired level and through which the oil and refrigerant may flow, and wherein said tube sheet has an imperforate portion which forms a bottom wall beneath said oil-collection space.

6. Apparatus as described in claim 5 which includes means forming a horizontal bulb well at substantially said desired level to which liquid refrigerant passes and from which gas refrigerant flows to said chamber, and wherein said control means includes a control unit having a temperature-sensing bulb positioned within said well.

7. Apparatus as described in claim 1 wherein said evaporator comprises, a vertical shell, a pair of tube sheets positioned respectively near the bottom of said shell to provide a refrigerant inlet header end at the bottom of said chamber, and a plurality of refrigerant tubes each mounted at its ends respectively in said tube sheets to provide for refrigerant to pass upwardly through said tubes from said header to said chamber, and means to direct fluid to be cooled through said shell between said tube sheets and around said tubes.

8. Apparatus as described in claim 7 wherein said oil separating means comprises a skimmer cup mounted upon the tube sheet at the bottom of said chamber, and

wherein said suction tube means includes a tube having its lower end positioned at the upper portion of said skimmer cup and having inverted V-notches therein, said tube being mounted in the top of said shell and having a horizontal portion through which the suction gas and oil pass to said suction line.

9. In a refrigeration system having a compressor from which oil passes with compressed refrigerant and having evaporator means within which the refrigerant is evaporated along vertical paths and the oil tends to accumulate above said paths, means to deliver the refrigerant gas and the oil from the evaporator to a suction line extending to the compressor, comprising, means forming a header chamber into which the refrigerant gas passes after being evaporated, and including a bottom portion which provides a space within which a body of liquid refrigerant and oil accumulates, control means to maintain a desired level of said body of liquid refrigerant and oil, annular baffle means forming an oil collection space within which a relatively quiescent body of liquid may accumulate and having means forming edges past which the oil flows relatively free of liquid refrigerant, suction tube means having an opening positioned at said annular baffle means providing a path for the free fiow of refrigerant gas to flow downwardly to said opening, whereby refrigerant gas flowing into said tube means entrains oil with it.

References Cited UNITED STATES PATENTS 3,111,819 11/1963 Williams 6 2503 3,304,741 2/1967 Weller 62471 MEYER PERLIN, Primary Examiner.

U.S. Cl. X.R. 

